Scaling Your Chart
One extra feature that you would almost certainly need to have is the ability
to "scale" the bars. Say that the numbers for NBC, CBS, and CNN were 3000, 2000,
and 3200, then you could not directly use these numbers as the number of pixels
for the bar lengths. What you would have to define is how much one pixel should
represent. For the latter numbers you could define the scale like this: 1 pixel
equals 10 of your units. Thereby the value 3000 would become 300 pixels. A new
bean-method could handle this:
public void setScale(float scale)
In the example above we would use it like this:
<%=graph.setScale(10)%>
Note that the scale is of type "float", which allows us to specify a scale
like "0.1F", meaning that one of our units equals 10 pixels.
Adding Other Features
It's very easy to add some simple effects to the bars by utilizing well-known
HTML-features:
- a "tool-tip" can be added to a bar by using the title-option on the
img-tag. This could be used to give further information on the poll results.
- mouseover/mouseout effects can be added to the bars. This allows you to
call JavaScript functions which could be used for other visual effects.
To support older Explorer and Netscape versions you would have to make a
hyperlink around the bar-image and then apply the title-option and mouse-events
to this hyperlink.
Improving the Bar Charts Further
In the next article I'll show how to make the charts more professional, e.g.
by adding an axis, and also how to facilitate using them by making some
high-level methods that completely hide the table structures.
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